Epicyclic gear systems, often called planetary systems, have the capacity to transmit considerable power in confined spaces. Typical of such confined spaces are the nacelles of wind turbines. In a wind turbine a rotor driven by blades that catch the wind powers an electrical generator. But the rotor revolves slowly, while the generator must turn at a considerably higher velocity if it is to remain relatively small. To this end, a transmission exists between the rotor and the generator to increase the speed. Usually the transmission contains one or more epicyclic gear sets. The transmission must have a high power density.
In its most basic form an epicyclic gear system has a sun gear and a ring gear located around the sun gear, with both centered along a common central axis. Planet gears located between the sun and ring gears engage both and rotate about pins that establish axes that are offset from the central axis. The pins form part of a carrier that likewise shares the central axis.
The carrier may take the form of the straddle variety in which each pin extends between and is anchored in walls at both of ends of the carrier. On the other hand, the carrier may be of the flexpin variety in which each flexpin has an inner pin that extends from a carrier wall in a cantilevered manner and at its remote end is fitted with a sleeve that doubles back over the inner pin such that it is cantilevered from the remote end of the inner pin—a double cantilever so to speak. See U.S. Pat. No. 3,309,743 to R. J. Hicks.
Straddle carriers under heavy loads experience torsional wind up which causes one carrier wall to twist slightly ahead of the other carrier wall, thus skewing the pins and changing a mesh between the planet gears and the sun and ring gears. This leads to excessive noise, friction and wear. In a flexpin carrier, the inner pin of each flexpin skews in one direction, while the sleeve skews in the opposite direction to negate the skew of the inner pin. While this mitigates the skewing problem, the inner pins are heavily stressed where they are cantilevered from the carrier wall.